AIM: To study the neonatal outcome of infants exposed to buprenorphine in utero. METHODS: We prospectively followed 54 buprenorphine-using pregnant women and their 58 infants. Urinary buprenorphine and norbuprenorphine concentrations in the mothers were measured prior to delivery, and in the infants during the first 3 days of life. The Finnegan score was used to evaluate neonatal abstinence syndrome. Other medical problems as well as social outcomes were recorded. RESULTS: All infants had buprenorphine in their urine. A total of 38 infants required 20 +/- 10 days (range 7-48 days) of morphine treatment for neonatal abstinence syndrome. The length of hospital stay for all infants was 25 +/- 19 days (range 3-125 days). The infants' highest urinary norbuprenorphine concentrations across their first 3 days of life correlated with the length of hospital stay and duration of morphine treatment (both p < 0.05). The mean birth weight and mean head circumference (n = 58) were below average (mean -0.7 standard deviation [SD] and mean -0.5 SD, respectively). Eleven infants were discharged home, 19 infants were placed in foster care and 28 infants were discharged with their mothers to Mother and Child homes or to other institutions. CONCLUSION: Maternal buprenorphine use at the time of birth may cause neonatal abstinence syndrome, requiring long-term hospitalization. Multiple social problems require a multidisciplinary team approach.